Layered microelectronic contact and method for fabricating same

ABSTRACT

A microelectronic spring contact for making electrical contact between a device and a mating substrate and method of making the same are disclosed. The spring contact has a compliant pad adhered to a substrate of the device and spaced apart from a terminal of the device. The compliant pad has a base adhered to the substrate, and side surfaces extending away from the substrate and tapering to a smaller end area distal from the substrate. A trace extends from the terminal of the device over the compliant pad to its end area. At least a portion of the compliant pad end area is covered by the trace, and a portion of the trace that is over the compliant pad is supported by the compliant pad. A horizontal microelectronic spring contact and method of making the same are also disclosed. The horizontal spring contact has a rigid trace attached at a first end to a terminal of a substrate. The trace is free from attachment at its second end, and extends from the terminal in a direction substantially parallel to a surface of the substrate to the second end. At least a distal portion of the trace extending to the second end is spaced apart from the surface of the substrate. The spaced-apart distal portion is flexible in a plane parallel to the substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to microelectronic contacts for use withsemiconductor devices and the like.

2. Description of Related Art

The demand for ever-smaller and more sophisticated electronic componentshas driven a need for smaller and more complex integrated circuits(ICs). The ever-smaller ICs and high lead counts, in turn, require moresophisticated electrical connection schemes, both in packaging forpermanent or semi-permanent attachment, and for readily demountableapplications such as testing and burn-in.

For example, many modern IC packages have smaller footprints, higherlead counts and better electrical and thermal performance than ICpackages commonly used only a few years ago. One such compact IC packageis the ball grid array (BGA) package. A BGA package is typically arectangular package with terminals, normally in the form of an array ofsolder balls, protruding from the bottom of the package. These terminalsare designed to be mounted onto a plurality of bonding pads located onthe surface of a printed circuit board (PCB) or other suitablesubstrate. The solder balls of the array are caused to reflow and bondwith bonding pads (terminals) on a mating component, such as by passingthe component with the mounted BGA package through an ultrasound chamberor like thermal energy source, and then removing the energy source tocool and harden the solder and form a relatively permanent bond. Oncemelted and re-hardened, the solder ball connections cannot readily bere-used, if at all. Hence, separate, readily demountable contactelements are required to contact the terminal pads of the IC or thesolder balls of the BGA package during testing and burn-in.

The advantages of readily demountable contact elements for use incompact packaging and connection schemes have previously beenrecognized. Readily demountable, flexible and resilient microelectronicspring contacts for mounting directly to substrates such as ICs aredescribed in U.S. Pat. No. 5,917,707 to Khandros et al. Among otherthings, the '707 patent discloses microelectronic spring contacts thatare made using a wire bonding process that involves bonding a very finewire to a substrate, and subsequent electro-plating of the wire to forma resilient element. These microelectronic contacts have providedsubstantial advantages in applications such as back-end waferprocessing, and particularly for use as contact structures for probecards, where they have replaced fine tungsten wires. These same orsimilar contact elements may also be used to make electrical connectionsbetween semiconductor devices in general, for making both temporary(readily demountable) and more permanent electrical connections inalmost every type of electronic device.

Presently, however, the cost of fabricating fine-pitch spring contactshas limited their range of applicability to less cost-sensitiveapplications. Much of the fabrication cost is associated withmanufacturing equipment and process time. Contacts as described in theaforementioned patents are fabricated in a serial process (i.e., one ata time) that cannot be readily converted into a parallel, many-at-a-timeprocess. Thus, new types of contact structures, referred to herein aslithographic type microelectronic spring contacts, have been developed,using lithographic manufacturing processes that are well suited forproducing multiple spring structures in parallel, thereby greatlyreducing the cost associated with each contact.

Exemplary lithographic type spring contacts, and processes for makingthem, are described in the commonly owned, co-pending U.S. patentapplications Ser. No. 09/032,473 filed Feb. 26, 1998, by Pedersen andKhandros, entitled LITHOGRAPHICALLY DEFINED MICROELECTRONIC CONTACTSTRUCTURES,” and Ser. No. 60/073,679, filed Feb. 4, 1998, by Pedersenand Khandros, entitled “MICROELECTRONIC CONTACT STRUCTURES.” Theseapplications disclose methods for fabricating the spring structuresusing a series of lithographic steps, thereby building up the height ofthe spring contact with several layers of plated metal that may bepatterned using various lithographic techniques. Microelectronic springcontacts are preferably provided with ample height to compensate for anyunevenness in the mounting substrate and to provide space for mountingcomponents, such as capacitors, under the spring contact.

Methods of achieving adequate height in a single lithographic step,i.e., a single resilient layer, and exemplary structures made thereby,are disclosed in the commonly owned, co-pending U.S. patent applicationsSer. No. 09/364,788, filed Jul. 30, 1999 by Eldridge and Mathieu,entitled “INTERCONNECT ASSEMBLIES AND METHODS,” and Ser. No. 09/710,539,filed Nov. 9, 2000, by Eldridge and Wenzel, entitled “LITHOGRAPHIC SCALEMICROELECTRONIC SPRING STRUCTURES WITH IMPROVED CONTOURS.” The foregoingapplications disclose spring elements made from a single layer of metal.The metal layer is plated over a patterned three-dimensional layer ofsacrificial material, which has been shaped using a micromachining ormolding process. The sacrificial layer is then removed, leaving afree-standing spring contact having the contoured shape of the removedlayer.

A need therefore exists for an improved microelectronic spring contact,and method of making it, that achieves or improves upon the performanceof multi-layer and single-layer spring contacts at a substantially lowercost. The spring contact should be useful in very dense fine-pitcharrays for directly connecting to IC's and like devices, and be capableof making both relatively demountable and relatively permanent (e.g.,soldered) connections.

Moreover, it is desirable that the microelectronic spring contact beuseful in compact packaging schemes, where low cost, demountability, andresiliency are important. Exemplary applications may include portableelectronic components (cellular phones, palm computers, pagers, diskdrives, etc.), that require packages smaller than BGA packages. For suchapplications, solder bumps are sometimes deposited directly onto thesurface of an IC itself and used for attachment to the printed circuitboard (PCB). This approach is commonly referred to as direct chip attachor flip-chip. The flip-chip approach is subject to variousdisadvantages.

One key disadvantage is the requirement for a polymer underfill beneatha die. The underfill is required to reduce thermal stresses caused bythe relatively low thermal expansion of the silicon die relative to thetypically much higher expansion of resin-based PCB's. The presence ofthe underfill often makes it infeasible to rework the component.Consequently, if the IC or its connection to the PCB is defective, theentire PCB usually must be discarded.

Another type of BGA package, the chip-scale ball grid array or a chipscale package (CSP), has been developed to overcome this disadvantage offlip-chips. In a chip scale package, solder ball terminals are typicallydisposed underneath a semiconductor die in order to reduce package size,and additional packaging elements are present to eliminate the need forunderfill. For example, in some CSP's, a soft compliant elastomer layer(or elastomer pad) is disposed between the die and the solder ballterminals. The solder ball terminals may be mounted onto a thin 2-layerflex circuit, or mounted to terminals on the complaint member. The IC istypically connected to terminals on the flex circuit or elastic memberusing a wire or tab lead, and the entire assembly (except the ball gridarray) is encapsulated in a suitable resin.

The elastomeric member is typically a polymer, such as silicone, about125 μm to 175 μm (5-7 mils) thick. The elastomer pad or layeressentially performs the function of and replaces the underfill used inflip-chips, that is, minimizes thermal mismatch stress between the dieand the PCB. In other CSP designs, the IC is adhered directly to thesurface of a two-layer flex circuit, and connected to terminals on thechip side of the flex circuit using wire leads. Solder balls are mountedon an opposite surface of the flex circuit. This design lacks anelastomer layer for decoupling the die from the PCB and, therefore, maynot eliminate the need for underfill.

Current chip-scale package designs have a number of shortcomings. Theelastomeric materials tend to absorb moisture, and if excessive moistureis absorbed, rapid outgassing of this moisture at reflow temperaturesmay cause the formation of voids in the elastomer layer, or bursting ofthe package. For example, moisture may be released from polymermaterials in the elastomer and become trapped within the die attachmentadhesive. Voids may then be formed when this trapped moisture expandsduring board assembly heating operations, typically causing cracking andpackage failure. Formation of such voids may be particularly problematicduring reflow attachment to a PCB.

Another difficulty with chip-scale package designs is the process forintegrating the elastomer member, which is typically done by picking andplacing elastomer pads onto individual sites, or by screen printing andsubsequently curing a fluid polymer. In either case, it may be difficultto meet the tight tolerances and package flatness required for a CSPapplication. For example, in a typical CSP design, the package flatness(planarity) should be less than about 25 μm (1 mil) to ensure that allsolder balls establish contact with PCB upon reflow. This level offlatness may be difficult to achieve using prior art processes fordepositing the elastomeric materials.

Therefore, it is further desirable to provide an improvedmicroelectronic contact element for applications such as CSPs andflip-chips.

SUMMARY OF THE INVENTION

The structure of the spring contacts according to the present inventionmay be understood by considering an exemplary method by which they maybe fabricated. In an initial step of the method, a precisely shaped pit,such as a pyramidal pit, is formed in a sacrificial substrate using anysuitable technique, for example, etching or embossing. Typically, alarge array of identical pits will be formed at the same time in thesacrificial substrate, arranged in a pattern corresponding to thedesired position of the contact tips to be formed on the electronicdevice. The surface of the pits may then be coated, if necessary, with athin layer of a suitable release material, such aspolytetrafluoroethylene (PTFE). The pits may then be filled with asuitable fluid elastomer, or similar compliant material. The elastomeror compliant material is preferably free of any filler materials, suchas conductive fillers. The sacrificial substrate may then be mated tothe device substrate on which the spring contacts are to be formed, theelastomer cured (solidified) in place, thereby adhering the elastomer tothe device, and the sacrificial substrate removed. In the alternative,the elastomer or compliant material may be cured before the sacrificialsubstrate is mated to the device substrate, and the compliant membersadhered to the device process by some other method, such as applicationof heat or by a suitable adhesive. As yet another alternative, dots of apolymer material may be applied to the device substrate by, for example,screen printing, and the pit features then pressed against the dots tomold the dots.

As a consequence of the foregoing steps, the device substrate should bepopulated with at least one compliant pad or protrusion, and typically,a plurality of compliant pads, positioned away from the workingterminals of the device substrate. For most applications, the pads arepreferably of similar or nearly identical height and shape, having arelatively wide base and a pointed top. Of course, the pads may bedifferent sizes and/or shapes depending on the requirements of theintended application. Suitable shapes may include pyramids, truncatedpyramids, stepped pyramids, prisms, cones, quadrangular solids, andsimilar shapes. The pads may be essentially solid and homogenous, or mayinclude voids, bubbles, layers, and the like. It is not necessary thatconductive contact be established between the compliant members and thedevice substrate. To the contrary, the compliant members are preferablypositioned so as avoid contact with terminals on the device substrate.Also, the compliant pads will generally be distributed in apitch-spreading pattern relative to the terminals on the devicesubstrate.

In an embodiment of the invention, the compliant pads are primarilyelastic, meaning that they are configured to spring back to theiroriginal positions after an applied load is removed. In alternativeembodiments, the compliant pads may be primarily inelastic, meaning thatthey will not spring back to their original positions after the appliedload is removed; or the compliant pads may be configured to exhibit somecombination of elastic and inelastic behavior. One of ordinary skill mayselect different materials and pad geometries to obtain the desiredresponse characteristics under anticipated load conditions.

In an embodiment of the invention, the device substrate, including theprotrusions, may be coated with a thin metallic seed layer, such as atitanium-tungsten layer, applied by any suitable process such assputtering. One or more uniform conformal layers of a sacrificialmaterial, such as an electrophoretic resist material, is then appliedover the device substrate. The sacrificial layer is then patterned asdesired to expose the seed layer in a pattern of traces extending fromthe terminals of the device substrate to respective tops of thecompliant pads. The trace pattern may be made wider over the compliantpads for greater stiffness and strength of the resulting contactstructures.

A metallic resilient and/or conductive layer is then plated to thedesired depth over the partially exposed seed layer. Nickel or nickelalloy material is generally preferred, plated to a depth sufficient tobe suitably strong and resilient. In an embodiment, the nickel materialis plated to sufficient depth so the resulting trace is stiffer than thecompliant pads. Optionally, the resilient layer is coated with aprotective and conductive layer, such as a thin layer of gold, after theplating step. After the desired metallic layers are applied, the layerof sacrificial material and the excess seed layer are removed usingprocesses that leave the compliant protrusions and metal traces on thedevice substrate.

The resulting structure is then ready to use without further processing,and comprises a metal trace integral with a spring contact running fromeach desired terminal of the device substrate to the top of a respectiveone of the compliant pads. Preferably, a pointed top of each compliantpad has imparted a relatively sharp pointed tip to each spring contactby the highly conformal plating process. Each contact extends bothlaterally and vertically from the base of each compliant pad to the topof each pad, providing a cantilevered structure that imparts abeneficial wiping action to the motion of the contact tip when thespring contact is deflected. The spring contacts are advantageouslysupported by the compliant pad during use.

The support of the compliant material may enable use of a thinner platedlayer for the spring contacts than would otherwise be required toprovide adequate contact forces. The thinner plated layer, in turn, maysave substantial processing time during the plating step. Also, theforegoing method avoids any need for contouring or molding of asacrificial layer, any need for separate forming steps for providing asharp contact tip, and any need for a separate step to provideredistribution traces.

In an alternative embodiment, the plating step and the related steps ofapplying the seed layer and applying and patterning the resist layer areomitted. Instead, the desired traces and contact elements are patterneddirectly onto the device substrate and elastomer protrusions by a methodsuch as sputtering or vapor deposition.

In another alternative embodiment, the traces are configured for aflip-chip application that requires no elastomer pad or underfill. Thetraces are shaped to be resilient in a direction parallel to the devicesubstrate. For convenience, such traces are referred to herein as“horizontal springs,” and it should be apparent that “horizontal” is notlimiting except in the sense of describing resiliency in the directionparallel to the device substrate. The horizontal resiliency compensatesfor thermal mismatch between the device substrate and the PCB or othermember to which it is mounted, and thereby eliminates the requirementfor underfill and for elastomer members. Optionally, the traces may alsobe made resilient in a direction perpendicular to the device substrate,like the spring contacts described in the references cited above.

Preferably, the horizontal spring contacts are formed on a sacrificiallayer on the device substrate. Each horizontal spring contact runsbetween a terminal of the device and a bonding pad, such as a pad forbonding to a corresponding pad of a PCB using a solder ball or adhesiveconnection. Horizontal flexibility may be provided by patterning thetrace in any suitable fashion, such as in a zigzag, pleated, crenulated,or serpentine pattern. The sacrificial layer is then removed, leavingeach horizontal spring contact suspended above the device substrate,except where it is attached to its respective terminal. Each trace isthus made flexible in the direction parallel to the device substrate.When the free end of each trace is bonded to a mating substrate, stressarising from thermal mismatch between the device and the matingsubstrate is relieved by deflection of the horizontal spring contacts.Optionally, a compliant pad may be located under a contact tip of thehorizontal spring contact, for additional vertical support.

A more complete understanding of the layered microelectronic contact andthe horizontal spring contact will be afforded to those skilled in theart, as well as a realization of additional advantages and objectsthereof, by a consideration of the following detailed description of thepreferred embodiment. Reference will be made to the appended sheets ofdrawings which will first be described briefly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged perspective view of an exemplary microelectronicspring contact according to the invention with a pyramidal compliantpad.

FIG. 2 is an enlarged plan view of an array of microelectronic springcontacts of the type shown in FIG. 1, showing a portion of apitch-spreading array.

FIG. 3 is an enlarged perspective view of exemplary microelectronicspring contacts using a shared prism-shaped compliant pad.

FIG. 4 is an enlarged perspective view of an exemplary microelectronicspring contact using a hemispherical compliant pad.

FIG. 5 is an enlarged perspective view of an exemplary microelectronicspring contact using a conical compliant pad.

FIG. 6 is an enlarged side view of an exemplary microelectronic springcontact using a compliant pad in the shape of a stepped pyramid.

FIG. 7 is an enlarged side view of an exemplary microelectronic springcontact using a compliant pad in the shape of a truncated pyramid.

FIG. 8 is an enlarged side view of an exemplary microelectronic springcontact with a pyramidal compliant pad, showing deflectioncharacteristics of a spring contact having a metallic trace that isrelatively stiff compared to the compliant pad.

FIG. 9 is an enlarged side view of an exemplary microelectronic springcontact with a pyramidal compliant pad, showing deflectioncharacteristics of a spring contact having a metallic trace that isrelatively flexible compared to the compliant pad.

FIG. 10 is a flow diagram of showing exemplary steps of a method forforming a microelectronic spring contact according to the invention.

FIG. 11 is a flow diagram showing exemplary steps of a method fordepositing a conductive trace between a terminal and a compliant pad.

FIG. 12 is an enlarged plan view of an exemplary microelectronic springcontact having a relatively thin and flexible metal trace deposited overa pyramidal compliant pad.

FIG. 13 is an enlarged perspective view of the spring contact shown inFIG. 12.

FIG. 14 is an enlarged perspective view of a spring contact with offsetopenings in a relatively thin and flexible metal trace, for enhancedlateral flexibility.

FIG. 15A is a plan view of an exemplary flip-chip semiconductor devicehaving an array of microelectronic spring contacts according to theinvention.

FIG. 15B is an enlarged plan view of the flip-chip device shown in FIG.15A.

FIG. 16 is an enlarged side view of an exemplary flip-chip device withreadily demountable microelectronic spring contacts according to theinvention.

FIG. 17 is an enlarged side view of an exemplary flip-chip device withsolderable microelectronic spring contacts according to the invention.

FIG. 18 is an enlarged perspective view of a horizontal spring contactaccording to the invention.

FIG. 19 is an enlarged plan view of a serpentine horizontal springcontact according to the invention.

FIG. 20 is an enlarged plan view of a horizontal spring contact having ahairpin-shaped beam portion.

FIG. 21 is a flow diagram showing exemplary steps of a method for makinghorizontal spring contacts according to the invention.

FIG. 22 is an enlarged plan view of an exemplary flip-chip device withan array of horizontal spring contacts.

FIG. 23 is an enlarged side view of the flip-chip device shown in FIG.22 in contact with terminals of a substrate.

FIG. 24 is an enlarged perspective view of a horizontal spring contactin combination with a pyramidal compliant pad.

FIG. 25 is an enlarged side view of a horizontal spring contact incombination with a compliant pad in the shape of a truncated pyramid.

FIG. 26 is an enlarged perspective view of a horizontal spring contactin combination with a compliant pad in the shape of a stepped pyramid.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides microelectronic spring contacts thatovercome limitations of prior art spring contacts. In the detaileddescription that follows, like element numerals are used to describelike elements appearing in one or more of the figures.

The present invention achieves the benefits of multi-layer andsingle-layer lithographic spring contacts as disclosed in the patentapplications referenced herein, at a potentially lower cost, andprovides additional advantages for certain packaging and connectingapplications. The spring contacts of the present invention are believedespecially suitable for compact packaging applications, such asflip-chip packages and CSP's, where they may replace or augment the useof ball grid arrays as connection elements.

With proper selection of materials, the spring contacts may also be usedfor testing and burn-in applications. It is therefore within the scopeand intent of the invention that spring contacts according to theinvention be fabricated directly on the devices of an unsingulated waferfor initial testing and/or burn-in; remain on the devices after testingfor burn-in testing before or after packaging, if desired; and then beused as the primary connection element (i.e., with or without solder orconductive adhesive) for final assembly to an electronic component. Inthe alternative, the spring contacts of the present invention may beused for any selected one or combination of the foregoing applications,used as secondary connection elements (e.g., IC to flex circuit) withina package incorporating other connection elements such as a BGA, used asthe contact elements or interposer elements of a test probe, used withina connector such as a Land Grid Array (LGA) socket, or for any othersuitable connection application.

An exemplary layered microelectronic spring contact 100 is shown inFIG. 1. Spring contact 100 comprises two primary layers of material: afirst non-conductive elastomer layer in the form of pyramidal compliantpad I 10, and a second conductive and resilient layer in the form ofmetallic trace 102. Spring contact 100 is described as layered becauseat least a part of a conductive layer (trace 102) overlies anon-conductive layer (pad 110) and the two layers together define thecontact 100.

Compliant pad 10 may be any suitable shape within the parametersdescribed herein. In an embodiment of the invention, it is a preciselyformed shape, such as a molded shape in alternative embodiments, pad 110may be a less well-defined shape, such as a relatively amorphous dollop.The morphology of the pad may be imparted to a relatively rigid metallictip and beam that are deposited over the pad surface. To ensure a highdegree of uniformity across densely populated spring contact arrays,each pad may be formed using a parallel process that minimizesvariability between pads. Parallel formation, such as molding en masse,provides the further benefit of requiring less time than individualdollop formation.

Specifically, pad 110 has a pyramid shape, although other suitableshapes may be used such as, for example, the pad shapes describedherein. In more general terms, the pad 110 may be described as a taperedmass having a relatively large and flat base area 112 where the pad isadhered to a substrate 116, and free side surfaces 109 that extend awayfrom the substrate and taper to a relatively small end area distal fromthe substrate. The end area is hidden from view in FIG. 1 by theoverlaying metallic tip 104. This tapered shape maximizes the area foradhesion to the substrate 116 while efficiently supporting a defined tipstructure. In this embodiment, the pyramidal shape reduce the potentialfor outgassing from the elastomeric material, to ventilate contact 100from any outgassing that may occur, and to provide increased lateralflexibility for thermal stress relief across contact arrays.

A pyramidal compliant pad may be particularly suitable because pyramidshapes with the desired tapered characteristics may readily be formedwith great precision and at extremely small scales by exploiting theproperties of commonly available crystalline silicon materials. It iswell known that a pyramidal pit, with side surfaces defined by theorientation of crystal planes in the silicon material, may readily beproduced by exposing a silicon substrate covered with a suitablypatterned layer of photo-resist to a suitable etchant, such as KOH. Anarray of substantially identical pyramidal pits may thus be produced ina silicon substrate, and the substrate with pits may be used as a moldfor forming an array of identical pyramidal compliant pads. Relatedshapes such as prisms, truncated pyramids or prisms, and steppedpyramids or prisms may be similarly formed using suitable etching andmasking process, as should be apparent to one of ordinary skill in theart.

Compliant pad 110 may be made of any suitable material. For example,suitable elastomer materials may include silicone rubber, naturalrubber, rubberized plastics, and a wide variety of other organic polymermaterials. One of ordinary skill in the art may select a suitablematerial by considering the intended operating environment (such astemperature or chemical environment) and desired structuralcharacteristics of the spring contact. For example, a suitably soft andresilient material may be selected once the contact geometry, desiredrange of compressibility, and maximum contact force are defined.Preferably, the pad material is a homogenous plastic material free ofany particulate filler material, and is inherently non-conductive.Homogenous plastic material may be more readily formed into a precisepad shape at small scales, such as for compliant pads that are less thanabout 5 mils (about 130 μm) wide.

The compliant pad 110 is adhered to substrate 116 at a location spacedapart from terminal 114 for which an electrical connection is desired. Aconductive trace 102 is then deposited from the terminal 1 14 to the endarea of the compliant pad, by a process such as electroplating. Trace102 may be comprised of any suitable metal or metal alloy, and mayinclude one or more layers. For example, trace 102 may be comprised of arelatively thick layer of nickel or nickel alloy for strength andrigidity, covered with a relatively thin layer of gold for conductivity.Trace 102 is preferably an integral piece of metal having a contact tipportion 104 deposited over the end area of pad 110, a pad-supported beamportion 106 running from the base 112 of pad 110 to the contact tip 104,and a substrate-supported redistribution trace portion 108 connectingthe beam portion 106 to the terminal 114. Contact tip 104 may berelatively pointed (as shown) for penetrating oxide and contaminationlayers of a mating terminal. In the alternative, the contact tip 104 maybe relatively flat for supporting features such as solder balls. Beamportion 106 may be tapered from a greater width at base 112 to anarrower neck at tip 104, as shown. This tapered design has theadvantage of more uniformly distributing stresses along the beam length.In the alternative, beam 106 may be of constant width, be provided witha reverse taper (wider at the top), or have any other suitable shape.Substrate 116 may be any suitable electronic device, including but notlimited to a semiconductor die or wafer, a connector or socket for a dieor wafer, and a printed circuit board.

Spring contacts 100 may readily be used in a pitch-spreading array 118,as shown in FIG. 2. Terminals 114 on substrate 116 are disposed at afirst pitch P1, and contact tips 104 are disposed at a coarser pitch P2,wherein P2 is greater than PI. FIG. 2 also shows various ways forpositioning the redistribution portion 108 of trace 102. As shown at thebottom right of FIG. 2, the redistribution trace 108 for a more distantcontact 100′ may be routed completely around the compliant pad 110 of acloser contact. In the alternative, as shown at the bottom left of FIG.2, trace 108 for a more distant contact 100″ may be deposited directlyover the compliant pad 110 of a less distant contact, adjacent to itsbase 112. Positioning traces over free areas of the compliant pads maybe advantageous in very dense arrays for which space for positioning theredistribution traces is limited. Such positioning may also relievestress in the materials from which the spring contact is formed.

FIGS. 3-7 show various alternative embodiments of the invention. FIG. 3shows a prism-shaped compliant pad 124 supporting a plurality of springcontacts 122. The end area of pad 112 is partially exposed. Otherfeatures of the contacts 122 are similar to those described for springcontact 100. FIG. 4 shows a spring contact 130 with a hemispherical pad132. Contact tip 104 is relatively flat. FIG. 5 shows a spring contact134 with a conical compliant pad 136. FIG. 6 is a side view of a springcontact 140 having a compliant pad 142 in the shape of a steppedpyramid. Compared to a regular pad, the stepped pyramid pad 142 providesa lower aspect ratio, that is, a lower height for a base of given size.The lower aspect ratio may be advantageous for providing a firmercontact for applications in which a higher contact force is desired.FIG. 7 shows a side view of a spring contact 150 having a compliant pad152 in the shape of a truncated pyramid. The truncated pyramid shapealso provides a lower aspect ratio pad, and may be suitable forapplications in which a flat contact tip 104 is desired. Spring contactsmay be provided in various other shapes and configurations differentfrom those depicted herein, without departing from the scope of theinvention.

The relative structural properties of the compliant pad and theoverlying conductive trace may be varied. In an embodiment of theinvention, the compliant pad is relatively soft and flexible compared tothe conductive trace. FIG. 8 shows a deflection mode of a spring contact100 having a relatively flexible pad 110 and a relatively stiff beam106. In this embodiment, the characteristics of the spring contact 100are dominated by the properties of the beam 106, which will deflectunder the influence of a contact force in a mode similar to how it woulddeflect were it not supported by the compliant pad. The contact tip 104will accordingly move a lateral distance “dx” corresponding to avertical displacement “dz,” thereby providing a beneficial wiping actionto the contact tip.

In an alternative embodiment, the conductive trace can be maderelatively flexible compared to the compliant pad. FIG. 9 shows adeflection mode of a spring contact 160 having a pad-supported beam 166that is relatively flexible compared to compliant pad 162. To achievegreater flexibility, contact tip 164, beam 166 and redistribution trace168 may be deposited as a relatively thin layer, which advantageouslymay be accomplished more quickly than depositing a relatively thick beamlike beam 106. Being symmetrically supported, pad 162 will deflect avertical distance “dz” without appreciable lateral deflection. Beam 166and contact tip 164 bend to follow the contour of pad 162.

It should be appreciated that FIGS. 8 and 9 show deflection modes thatare at opposite ends of two extremes. It may be desirable to configure acontact that operates in a mode that is intermediate between the modesshown in FIGS. 8 and 9. In an intermediate mode, the spring contact willexhibit characteristics of both deflection modes. For example, thecontact tip will undergo some lateral deflection or wipe, while at thesame time being substantially supported by the compliant pad. Thus, inan intermediate mode the advantages of both deflection modes—i.e.,wiping action, and a thin, rapidly formed trace—may both be realized toa degree. One skilled in the art may construct a spring contact thatoperates in any desired deflection mode. For a given geometry andselection of materials, the beam thickness may be varied until thedesired deflection mode is achieved. Computer modeling may be useful inthe design phase to predict the deflection characteristics of aparticular spring contact design.

FIG. 10 shows exemplary steps of a method 200 for forming amicroelectronic spring contact according to the invention. In initialstep 202, a compliant pad is formed on a sacrificial substrate. To forman array of compliant pads, precision pits in a sacrificial substrate,such as a silicon substrate, in a pattern corresponding to the desiredarrangement of contact tips in the spring contact array that is to beformed. The precision pits are formed in a shape corresponding to thedesired shape of compliant pad, for example, a pyramidal pit is used toform a pyramidal pad, and so forth. Any suitable method may be used forforming the precision pits; in particular, various lithographic/etchingtechniques may be employed to form pits of various shapes. After thepits have been created, the sacrificial substrate is preferably coatedwith a thin layer of a suitable release agent, such as a PTFE materialor other fluoropolymer. An alternative method of forming a compliant padis by deposition of a dollop of uncured or softened elastomer materialdirectly on a substrate, and then curing or hardening the elastomer inplace.

After the sacrificial substrate has been prepared, the pits may befilled with the selected elastomeric material, preferably in a liquidstate. The substrate on which the contacts are to be formed (the “devicesubstrate”) may then be mounted to the sacrificial substrate, and theelastomeric material cured or hardened with the device substrate inplace, thereby adhering the compliant pads to the substrate. Thesubstrate and its attached pads may then be removed from the sacrificialsubstrate, transferring the pads to the device substrate as indicated atstep 204. The sacrificial substrate may be re-used as desired.

In the alternative, after the pits in the sacrificial substrate arefilled with the liquid elastomer, the elastomer material may be cured orhardened with the sacrificial substrate left free and open. Thesacrificial substrate may then be coated with a suitable adhesivematerial, thereby coating the exposed bases of the compliant pads.Preferably, the adhesive material is patternable, so that it may beremoved from the sacrificial substrate except in regions over theelastomer material. In addition, the adhesive material is preferablypressure-sensitive, so that it will adhere on contact with a matingsubstrate. The compliant pads may then be transferred to the devicesubstrate as desired.

With the compliant pads in place on the device substrate, at step 206, aconductive trace is deposited between a terminal of the device substrateand the top of a corresponding pad. FIG. 11 shows exemplary steps of amethod 210 for depositing a conductive trace on a device substrate andcompliant pad. At step 212, a seed layer is deposited over the entiresurface of the device substrate and its attached compliant pads. Onesuitable seed layer is a sputtered titanium-tungsten layer; a suitableseed layer may be selected by one skilled in the art.

At step 214, a sacrificial layer is deposited over the seed layer. Thesacrificial layer is a patternable material, such as a photoresistmaterial, and is preferably applied as a highly conformal layer over thedevice substrate and its protruding elastomeric pads. Various methodsmay be used to deposit a conformal layer of resist material. Onesuitable coating method for thicknesses up to about 35 μm iselectrodeposition (electrophoretic resist). Other methods may includespray coating, spin coating, or meniscus coating, in which a laminarflow of coating material is passed over the device substrate. A greaterdepth may be built up by successively coating and curing layers ofmaterial. The minimum depth of the sacrificial layer is preferably equalor greater than the desired thickness of the metallic trace to bedeposited.

At step 216, the sacrificial layer is patterned to expose the seed layerin the areas where the conductive traces are to be deposited. Generally,patterning may be accomplished using any suitable photo-patterningtechnique as known in the art. At step 218, the conductive tracematerial is deposited to the desired depth over the exposed areas of theseed layer, such as by electroplating. Successive layers of differentmaterials, such as a relatively thick layer of nickel or nickel alloy,followed by a relatively thin layer of gold or other suitable contactmetal such as palladium, platinum, silver, or alloys thereof, may beapplied as desired. At step 220, the sacrificial layer is removed, suchas by dissolving in a suitable solvent. The device is thereby providedwith an array of spring contacts according to the invention.

For spring contacts in which the metal trace is to be relatively thinand flexible, the metal trace need not be deposited by electroplating,and may preferably be deposited by a method such as sputtering or vapordeposition. In such case, the entire surface of the device substrate andcompliant pad may be coated with a thin layer or layers of metal to thedesired depth, as if with a seed layer. Then, a photoresist layer may beapplied and patterned to protect those areas of the device substratewhere a metallic trace layer is desired, and the remaining unprotectedareas of the metal layer removed in an etching step. By eliminating theelectroplating step, processing time may be substantially reduced forthose applications that do not require a relatively stiff metalliccontact element.

In the case of layered spring contacts with relatively thin and flexiblemetal layers, it may be advantageous to coat a greater proportion of thecompliant surface, up to and including the entire surface of thecompliant pad. An exemplary spring contact 170 with most of thecompliant pad 171 covered by a metallic layer 172 is shown in FIGS. 12and 13. Like the other spring contacts described herein, metal layer 172comprises a substrate-supported redistribution portion running between aterminal of the substrate and the base of the compliant pad 171, apad-supported portion 176 extending upwards from the base of the pad,and a contact tip 174 at the top of the compliant pad 171. In theexemplary contact 170, all four sides of the pyramidal pad 171 arecovered with the metal layer 172, except for a relatively small areaalong the four corners of the pyramid. Covering a greater proportion ofthe compliant pad advantageously lowers the resistivity of the contact170, and may also help protect the pad from damage. Openings in themetal layer over the compliant pad may be desirable for stress relief ofthe metal layer, to provide room for expansion (bulging) of the pad whendeformed, and to provide ventilation for outgassing. Stress relief mayalso be provided without using openings in the metal layer, such as byproviding metal layer 172 of a highly ductile material, such as gold.

FIG. 14 shows a spring contact 175 configured similarly to springcontact 170, but with laterally offset openings 177 positioned toprovide lateral flexibility for the pad-supported portions 179 of trace178. With suitably configured openings 177, the lateral flexibility ofcontact 175 may be increased. That is, contact 175 may be better able toaccommodate lateral deflection of its contact tip relative to its basewithout tearing of trace 178 or other failure of the spring contact.Lateral deflection forces may arise from thermal mismatch between thedevice substrate and a mating substrate, particularly when contact 175is soldered at its tip 174 to a mating substrate.

FIG. 15A shows a plan view of an exemplary flip-chip device 180 havingan array of microelectronic spring contacts 100 on a surface thereof. Anenlarged view of the same device 180 is shown in FIG. 15B. Each contact100 is connected to a terminal 114 of the device 180, as previouslydescribed. Device 180 may be a semiconductor device, such as a memorychip or microprocessor. Spring contacts 100 may be formed directly ondevice 180, preferably prior to singulation from the semiconductorwafer. Contacts 100 may then be used to connect to the device for bothtesting and assembly purposes. Although flip-chip mounting representsthe more compact design, it should be appreciated that contacts 100 maysimilarly be incorporated into CSP designs, if desired.

FIG. 16 shows a side view of device 180 in contact with a matingelectrical component 184, such as a printed circuit board. A contact tipof each contact 100 is in contact with a terminal 186 of component 184.A controlled amount of compressive force 182 may be applied using amounting frame or other fastening device, if it is desired to make theinstallation of device 180 readily demountable. The compressive force182 causes deflection of contacts 100 in a direction perpendicular tosubstrate 184, and in a lateral direction parallel to substrate 184. Thelateral deflection of contacts 100 may provide a beneficial wipingaction at the contact tips. Device 180 may be demounted as desired byreleasing the compressive force 182. If contacts 100 are not soldered toterminals 186, lateral stress from thermal mismatch between substrate184 and device 180 may be relieved by sliding between the contact tipsof contacts 100 and terminals 186. If contacts 100 are soldered inplace, it may be desirable to provide contacts with inherent lateralflexibility.

For example, contacts 170 of a type as shown in FIGS. 12-14 may beprovided on a device 190 that is to be soldered to a component 184, asshown in FIG. 17. The metallic portions of contacts 170 are relativelythin and flexible, and may be patterned for greater lateral flexibilityas described elsewhere herein. The metallic portions of contacts 170 arenot self-supporting, and rely on the compliant pad of each contact forsupport. Device 190 may be mounted to terminals 186 using dollops of asolder paste material 192. The compliant pad material used in contacts170 should be selected to withstand solder reflow temperaturesencountered during mounting. After being soldered, contacts 170 remaincapable of deflecting laterally at relatively low force levels forrelief of thermal stress. Also, ample space remains between contacts 170on device 190 for venting of the spring contact array, so the likelihoodof package failure by gas build-up an elastomer or other material of thecompliant pads may be reduced.

For some flip-chip and CSP applications, it may be desirable toeliminate the need for a compliant pad in the spring contact. A suitableself-supporting spring contact 300 for providing lateral resiliency inflip-chip and like applications without need for a compliant supportingpad is shown in FIG. 18. Spring contact 300 is an example of amicroelectronic spring contact of a type referred to herein as ahorizontal spring contact, meaning that the spring contact is primarilyresilient in a direction parallel to the surface of the substrate towhich it is mounted. Contact 300 comprises a base 306 attached tosubstrate 116, a cantilevered beam 304 running in a plane substantiallyparallel to substrate 116 and having at least one bend along its length,and a contact tip 302 configured for a solder attachment. Contact 300may be formed from an integral sheet of resilient and conductivematerial, such as a relatively thick nickel alloy trace deposited by amethod such as electroplating. Contact 300 may be coated with an outerlayer of a conductive metal, such as gold, or coated in any otherdesired way.

Various beam shapes may be suitable for horizontal spring contacts.FIGS. 19 and 20 show plan views of exemplary beam shapes that may besuitable. Referring to FIG. 19, spring contact 308 has a serpentine beam304. Each bend in the beam 304 may add additional resiliency in the lineof direction between base 306 and tip 302. Referring to FIG. 20, aseries of hairpin bends in beam 304 are used to provide resiliencybetween base 306 and tip 302 of spring contact 310. The hairpin designmay provide greater horizontal resiliency in a narrower space betweenthe base and tip. It should be apparent that numerous other shapes mayalso be suitable for beam 304. One skilled in the art may select asuitable shape that is suitably rigid and self-supporting in thevertical (perpendicular to substrate) direction while being sufficientlyflexible and resilient in the horizontal direction.

Exemplary steps of a method 250 for forming horizontal spring contactsaccording to the invention are shown in FIG. 21. At step 252, a firstsacrificial layer is deposited over a device substrate. At step 254, thefirst sacrificial layer is patterned to expose the terminals of thedevice substrate. Additional areas may be exposed in which structuresfor supporting the spring contacts (particularly those with long spans)may be formed. The first sacrificial layer may be any patternablematerial, such as a photoresist material used in the art ofphoto-lithography. It should be deposited in a layer of uniformthickness equal to the desired height of the horizontal springs abovethe substrate surface. The first sacrificial layer may then be patternedusing a photo-lithographic technique such as known in the art to exposean area of the substrate surface including and around the terminals ofthe device. The exposed area should be large enough to support thehorizontal spring that is to be constructed against its anticipatedvertical and horizontal loads.

After the terminals of the device have been exposed, and while most ofthe first sacrificial layer remains on the substrate, at step 256, aseed layer as previously described is deposited over the firstsacrificial layer and exposed terminal areas. At step 258, a secondsacrificial layer is deposited over the seed layer. The secondsacrificial layer should also be a photo-patternable material, andshould be deposited to a uniform depth equal to or greater than thedesired thickness of the horizontal spring material. At step 260, thesecond sacrificial layer is patterned in the desired shape of thehorizontal springs to be formed. The seed layer is exposed from eachterminal area along a beam running over the first horizontal layer to atip, which may be a pad-shaped tip.

A layer of conductive material is then deposited in the patterned secondsacrificial layer at step 262, such as by electroplating a metallicmaterial to the desired thickness. The conductive material willaccordingly be deposited only over the exposed seed areas to provide aspring contact structure of the desired shape. The conductive materialshould be selected according to the desired structural and electricalproperties of the horizontal spring contacts. For example, a nickel ornickel alloy material could be selected as the primary structuralmaterial for strength and resiliency, and a secondary layer of a moreconductive material, such as gold, could be applied as a top layer. Oneskilled in the art will recognize other suitable materials andcombinations of materials, that may be applied in any number of layers.After the conductive material or materials have been deposited, thefirst and second sacrificial layers are removed at step 264, such as bydissolution in a suitable solvent, to expose free standing horizontalspring contacts on the device substrate.

A plan view of an exemplary semiconductor device 312 provided with anarray 314 of horizontal spring contacts 300 is shown in FIG. 22. Device312 may be suitable for use in a flip-chip mounting application. Eachspring contact 300 has a base area 306 adhered to a terminal 316 ofdevice 312, a beam 304 running above and substantially parallel to thedevice substrate and having at least one bend, and a end area 302. Endarea 302 may be pad-shaped for accepting a solder ball or dollop ofsolder paste or other bonding material. The spring contacts 300 of array314 are arranged to provide a pitch-spreading redistribution scheme forterminals 316 of device 312. In the alternative, the contact tips 302 ofcontacts 300 may be arranged in a pitch-preserving or pitch-reducingreducing pattern.

FIG. 23 shows device 312 in a flip-chip mounting configuration to anelectronic component 184. A solder ball 192 is used to connect eachcontact tip 302 to a corresponding terminal 186 of component 184. Beams304 are generally parallel to the facing surfaces of device 312 andcomponent 184, while being held apart from both device 312 and component184, and free to flex along their length in a horizontal direction.Stress build-up by thermal mismatch between device 312 and component 184may thereby be mitigated by flexure of the horizontal spring contacts300. No elastomer material is needed to isolate the device from thecomponent, and the horizontal contacts 300 may be used for completesupport of device 312. In the alternative, auxiliary floating supports(not shown) may be used to support the device 312 above component 184,in which case contacts 300 may be made even more flexible.

Spring contacts may also be constructed that combine the characteristicsof pad-supported and horizontal spring contacts. FIG. 24 shows anexemplary combination spring contact 320, having a metallic trace 322lain over a prism-shaped compliant pad 329, and a wiping-type contacttip 324. Beam 326 is shaped in a zig-zag pattern over pad 329, forgreater horizontal flexibility. Various other horizontally flexibleshapes, e.g., serpentine, may also be used. A substrate-supportedterminal portion 328 extends directly from the base of the prism-shapedpad 329 over substrate 116.

In an alternative embodiment, a spring contact may be provided with ahorizontally flexible portion extending from above the base of acompliant pad to a terminal of a substrate. FIGS. 25 and 26 show springcontacts 330, 350 of this general type. A side view of a terminal 330having a compliant pad 152 of a truncated pyramidal shape is shown inFIG. 25. Metallic trace 332 comprises: a contact tip 334 at the top ofthe compliant pad 152; a pad-supported portion 340 connected to thecontact tip 334; an end-supported portion 342 having multiple bends 344connected to portion 340 and extending from the compliant pad 152,running above and free from substrate 116; and a substrate-supportedportion 338 connecting portion 342 to a terminal of substrate 116.Because its contact tip 334 is supported by the compliant pad 152, trace332 may be made more flexible than might otherwise be possible. Beingthinner and more flexible, end-supported beam portion 342 may providegreater horizontal flexibility as compared to a cantilevered structurelike spring contact 300 shown in FIG. 18. A spring contact of the tykeshown in FIG. 25 may thus be especially preferred for applicationsrequiring greater mitigation of horizontal thermal stresses and whereinthe presence of a compliant pad is not problematic.

A similar combination contact 350, utilizing a stepped pyramidalcompliant pad 352, is shown in FIG. 26. The contact tip 334 is providedwith a solder ball 192 for subsequent attachment to a componentsubstrate. Pad-supported trace portion 340 follows the contours of thepad 352 to a point adjacent to and above its base. From there, anend-supported portion 342 with two bends 344 extends to asubstrate-supported pad 338 on substrate 116. Spring contact 350 may bemade relatively firm and stable in the vertical direction by itssupporting pad 352, while retaining a high degree of flexibility in aplane parallel to the substrate 116 by its flexible, end-supportedportion 342.

A second trace portion 356 is also shown in FIG. 26. Second traceportion 356 runs over a portion of compliant pad 352 to a secondcompliant pad and a second contact tip. The second pad and tip are notshown in FIG. 26, but may be similar to pad 352 and contact tip 334, ormay be differently configured.

One skilled in the art may construct a spring contact of the type shownin FIGS. 25-26 by suitably combining the steps of methods 200 and 250described herein. For example, the end-supported portion may be formedby depositing a first resist layer over a pad (e.g., 152 or 352) and asubstrate 116, and then selectively removing regions of the first resistlayer over the pad and terminal. A seed layer may then be deposited overthe first resist layer and the exposed areas of pad and terminal. Then,a second resist layer is deposited over the seed layer and patterned toreveal the seed layer in the pattern of the desired traces. The tracesare then plated onto the exposed seed layer and the resist layers areremoved to reveal a contact like contacts 330, 350.

Having thus described a preferred embodiment of the layeredmicroelectronic contact and the horizontal spring contact, it should beapparent to those skilled in the art that certain advantages of thewithin system have been achieved. It should also be appreciated thatvarious modifications, adaptations, and alternative embodiments thereofmay be made within the scope and spirit of the present invention. Forexample, particular shapes of compliant pads and horizontal springcontacts have been illustrated, but it should be apparent that theinventive concepts described above would be equally applicable to othershapes and configurations of pads and metallic elements having thegeneral properties described herein.

As another example, the spring contacts described herein may be usedwith any electronic component, including not only semiconductor devicesbut (without limitation) probe cards and other testing devices. As yetanother example, additional materials may be deposited on the springcontact structures described above; such materials enhancing thestrength, resiliency, conductivity, etc. of the spring contactstructures. As still another example, one or more layers of materialsmay be formed on the electronic component prior to or after creating thespring contact structures as described above. For example, one or morelayers of redistribution traces (separated by insulative layers) may beformed on the electronic component followed by formation of the springcontacts on the redistribution layer. As another example, the springcontacts may first be formed followed by formation of one or more layersof redistribution traces. Of course, all or part of the compliant layer(e.g., elastomeric layer) described with respect to any of the figuresmay be removed.

1-23. (canceled)
 24. A resilient microelectronic contact, comprising anat least partially self-supporting trace attached at a first end to aterminal of a substrate and free from attachment at a second endthereof, extending from the terminal to the second end, having at leasta distal portion extending to the second end spaced apart from thesurface of the substrate and free to flex in a plane parallel to thesurface of the substrate.
 25. The microelectronic contact of claim 24,wherein the distal portion has at least one bend for resiliency of thetrace in a plane parallel to the substrate.
 26. The microelectroniccontact of claim 24, wherein the distal portion of the trace ispatterned to follow a path having a shape selected from zigzag,crenulated, hair-pin shaped, and serpentine.
 27. The microelectroniccontact of claim 24, further comprising a contact tip connected to thesecond end of the rigid trace.
 28. The microelectronic contact of claim27, wherein the contact tip is flat and pad-shaped.
 29. Themicroelectronic contact of claim 27, further comprising a dollop ofbonding material on the contact tip.
 30. The microelectronic contact ofclaim 29, wherein the bonding material is a solder paste.
 31. Themicroelectronic contact of claim 27, further comprising a compliant paddisposed on the substrate under the contact tip.
 32. The microelectroniccontact of claim 31, wherein the compliant pad has a base adhered to thesubstrate, and side surfaces extending away from the substrate taperingto a end area distal from the substrate, wherein the end area issubstantially smaller than the base.
 33. The microelectronic contact ofclaim 31, wherein the compliant pad is at least partially supporting thecontact tip.
 34. A method for making a resilient microelectroniccontact, comprising: depositing a first layer of a sacrificial materialon a semiconductor device; patterning the first layer to expose aterminal of the device; depositing a conductive seed layer over thefirst layer and terminal; depositing a second layer of a sacrificialmaterial directly over the seed layer; patterning the second layer toexpose the seed layer along a path running from the terminal to aposition distal from the terminal; plating a metallic material along thepath of the exposed seed layer; and removing the first layer, the secondlayer, and an unplated portion of the seed layer, thereby exposing aresilient microelectronic contact attached at a first end to a terminalof a substrate and free from attachment at a second end thereof.
 35. Themethod of claim 34, wherein the patterning step further comprisesexposing the path having at least one bend.
 36. The method of claim 34,wherein the patterning step further comprises exposing the path having ashape selected from zigzag, crenulated, hairpin-shaped and serpentine.37. The method of claim 34, further comprising placing a dollop ofbonding material on the distal portion of the microelectronic contact.38. The method of claim 34, further comprising attaching a compliant padto the substrate prior to the first depositing step.
 39. The method ofclaim 38, wherein the attaching step further comprises attaching thecompliant pad having a base adhered to the semiconductor device, sidesurfaces extending away from the semiconductor device and tapering to aend area distal from the semiconductor device, wherein the end area issubstantially smaller than the base.
 40. The method of claim 39, whereinthe patterning step further comprises exposing the path leading to a tipportion of the compliant pad.
 41. A semiconductor device configured forflip-chip mounting to a substrate, comprising: a semiconductor devicehaving a plurality of terminals on a surface thereof; a plurality ofresilient microelectronic contacts, each comprising a rigid traceattached at a first end to each terminal of the device and free fromattachment at a second end thereof, extending from each terminal in adirection substantially parallel to the surface of the device to thesecond end, and having at least a distal portion extending to the secondend spaced apart from the surface and compliant in a plane parallel tothe surface of the semiconductor device.
 42. The semiconductor device ofclaim 41, wherein the plurality of terminals are spaced apart from oneanother for a first pitch distance within a first portion of thesurface, and wherein the surface has a second portion that isessentially free of terminals, the second portion being larger than thefirst portion.
 43. The semiconductor device of claim 42, wherein thesecond ends of the plurality of contacts are disposed over the secondportion of the surface and spaced apart from one another for a secondpitch distance, the second pitch distance being greater than the firstpitch distance.
 44. The semiconductor device of claim 41, wherein thedistal portion of each microelectronic contact has at least one bend forresiliency of the microelectronic contact in a direction parallel to thesubstrate.
 45. The semiconductor device of claim 41, wherein the distalportion of each microelectronic contact has a shape selected fromzigzag, crenulated, hairpin-shaped and serpentine.
 46. The semiconductordevice of claim 41, wherein the surface of the semiconductor device isessentially free of elastomer material.
 47. The semiconductor device ofclaim 41, further comprising a dollop of a bonding material disposed ona distal tip of the distal portion of each microelectronic contact. 48.The semiconductor device of claim 41, further comprising a compliant paddisposed between a distal tip of the distal portion of eachmicroelectronic contact and the substrate.
 49. The semiconductor deviceof claim 48, wherein the compliant pad has a base adhered to thesemiconductor device and side surfaces extending away from thesemiconductor device and tapering to a end area distal from thesemiconductor device, and wherein the end area is substantially smallerthan the base.